Hardness taper tube and production method and device therefor

ABSTRACT

An apparatus for manufacturing stiffness-taper tubing includes a die having an extrusion hole, a die holder for holding the die, and a mandrel mounted inside the die holder and that fits in the extrusion hole. The apparatus forms stiffness-taper tubing by switching between and supplying resins having different stiffnesses over the mandrel from a plurality of resin-supply ports formed in the die holder such that the stiffness gradually changes in the lengthwise direction. A mandrel insertion hole connecting to the extrusion hole is formed in the die holder and the mandrel is mounted in this mandrel insertion hole. The plurality of resin-supply ports open to a cylindrical space formed between the inner surface of the mandrel insertion hole and the outer surface of the mandrel at a position separated from the extrusion hole in the die, and the plurality of resins flow together in this space.

TECHNICAL FIELD

This invention relates to stiffness-taper tubing, that is formed byjoining two or more resin materials having different stiffness such thatthe stiffness along its length gradually changes, and to themanufacturing method and manufacturing apparatus for such tubing. Thestiffness-taper tubing of this invention is suitable for use in medicalapplications such as a catheter.

BACKGROUND ART

Conventionally, a two-layer extrusion-type formation apparatus was usedwhen using two types of resin materials having different stiffness toform stiffness-taper tubing. The stiffness-taper tubing was formed suchthat there was a stiff section made from a first resin, having muchstiffness in the longitudinal direction, a soft section made from asecond resin, having little stiffness, and a transition section betweenthese two sections in which the stiffness gradually changed (stiffnesstaper section). For this kind of stiffness-taper tubing, the first resinand then the second resin is supplied to the two-layer extrusion-typeformation apparatus, and the transition section is formed when switchingbetween resins and the first resin is gradually replaced by the secondresin.

When this kind of stiffness-taper tubing is used in medical applicationssuch as a catheter, a joint between both resin materials in thetransition section that is adequately strong is required, and it isdesired that the length of the transition section be long enough to beable to maintain its function as a catheter, but also be as short aspossible in order to improve operability.

FIG. 7 is a horizontal cross-sectional diagram of a two-layerextrusion-type formation apparatus that the inventors used beforedeveloping the present invention.

This two-layer extrusion-type formation apparatus 30 comprises a diehaving an extrusion hole 31, a die holder 34 for holding the die by wayof a bolt 33, and a mandrel 35 that is mounted such that it faces theextrusion hole 31. The mandrel 35 is attached to and held by the dieholder 34 by way of an inner-layer mandrel holder 36 and outer-layermandrel holder 37. The inner-layer and outer-layer mandrel holders 36,37 are nearly conical shaped, and there is a guide cavity 38 formed allthe way around the tip of the cone for supplying resin to the mandrel35.

On both of the outer sides of the die holder 34 there are switchingdevices 39, 49 for switching between and supplying the different typesof resins A and B. The switching devices 39, 40 are connectedrespectively to the resin A supply port 43 and resin B supply port 45,that are located on the die holder 34. There are heaters 47 on the dieholder 34 and switching devices 39, 40 for keeping the resins soft.

The switching device 39 for supplying resin A comprises a switchingvalve 41, and a resin A inlet 42 that is connected to the resin Aextruder. Resin A is supplied to the resin A supply port 43 on the dieholder 34 as the switching valve 41 turns. The resin A, that is suppliedto the resin A supply port 43, is supplied to a channel 49 in theouter-layer mandrel holder 37 by way of a connection path 44, and thensupplied to the guide cavity 38 on the tip by way of this channel 49 anddrawn out from the extrusion hole 31 by way of a ring-shaped space onthe outer surface of the mandrel 35.

Similarly, resin B passes through the resin B supply port and connectionpath 46 and is supplied to the guide cavity 38 by way of the channel 49in the inner-layer mandrel holder 36, and then is drawn out from theextrusion hole 31 by way of the ring-shaped space on the outer surfaceof the mandrel 35.

When either resin A or resin B is selected by the switching device 39,40 and supplied to the die holder 34, the resin that is not selectedpasses through the switching valve 41 of the respective switching device39 or 40 and is discharged through the resin discharge port (not shownin the figure). At that time, part of the resin that was not selectedremains in the resin supply ports 43, 45 of the switching devices 39, 40and the die holder 34, in the connection paths 44, 46, in the channelsin the inner-layer and outer-layer mandrel holders 36, 37 and in theguide cavity 38, and remains there until the resin is switched and fedagain.

The mandrel 35 is fastened to the end of a shaft 48. The center axis ofthis shaft 48 is coaxial with the center axis of the extrusion hole 31in the die 32. This shaft 48 is fastened to and held inside the dieholder 34 by fastening it on the inside of the inner-layer mandrelholder 36. During use, a core member passes along the axis of, forexample the shaft 48, mandrel 35 and extrusion hole 31, and meltedresin, that was selected by the switching device, is supplied from theextrusion hole 31 and flows around this core member to form tubing.

In this kind of two-layer extrusion-type formation apparatus 30, twokinds of resin are mixed at the point C in the figure where therespective cavity 38 opens up to the conical-shaped inlet of theextrusion hole 31 in the die 32, and the mixed resin is discharged in aformed shape from the outlet of the extrusion hole 31 at point D in thefigure. Moreover, when the two kinds of resins are alternately switchedand supplied to the die 32, at the time of switching, the first resinfills the space from the extrusion hole 31, between the mixing point Cat the die inlet and it the discharge point D at the die outlet, and themandrel 35. The resin that fills the space between this mixing point Cand discharge point D is then replaced by the next resin afterswitching. The transition section becomes the part from the start ofreplacement to the end of replacement.

However, in the inventor's prior 2-layer extrusion-type device, thecavities 38 for both the inner-layer 36 and outer layer 37 open up atthe mixing point C, so the volume between this mixing point C anddischarge point D becomes large, and as a consequence the length of thetransition section becomes long.

The length of the transition section is proportional to the timerequired for resin replacement. By taking the volume between the mixingpoint C and the discharge point D (called the joint-flow volume below)to be V, and taking the inflow rate of resin B, when going from 100%resin A to 100% resin B in this joint-flow volume V to be q, then thetime T required for replacement is given by the following equation:

 T=V/q+T1

(T1 is a constant that is determined by the mixing efficiency of resin Aand resin B.) Moreover, the time T required for replacement becomeslonger as the joint-flow volume V becomes larger. In other words, whenthe joint-flow volume V is large, the time T required for replacementbecomes long and the length of the transition section becomes long inaccordance.

Furthermore, in the prior two-layer extrusion-type formation apparatus,the resin supply path from the respective supply ports 43, 45 for resinA and resin B to the mixing point C becomes long and its volume becomeslarge. In addition, the amount of resin that remains in the resin supplypath during switching becomes large, and while waiting, this residualresin is heated by the heaters and there is a possibility that itsquality could be altered or become degraded.

Moreover, when forming stiffness-taper tubing with the prior two-layerextrusion-type formation apparatus, the second resin is supplied suchthat it pushes the residual first resin when the resin is switched, sothere is hardly any mixing between the two resins at the interfacebetween them, and the tubing is formed with a clear interface (contactplane) between the two resins. The two resins are joined with the tworesins in contact with each other through this kind of distinctinterface, so it is not possible to obtain adequate bonding strength,and there is the possibility that the tubing will come apart at thejoint surface in the transition section.

On the other hand, a catheter having a transition section in which thestiffness changes from a rigid section to a soft section has beendisclosed in U.S. Pat. No. 5533985, U.S. Pat. No. 5622665 and JapanesePat. No. H9-512445. In the transition section of the catheter in thesedisclosures, an interface with a wedge-shaped cross section is formed byswitching between two resin materials such that the first resin bitesinto the later resin. This kind of wedge-shaped contact surface wasformed probably due to the fact that there is very little mixing betweenthe two resins at the interface. When the two resins are joined withthis kind of surface contact, it is not possible to obtain adequatebonding strength, and there is the possibility that the tubing will comeapart at the wedge-shaped joint surface in the transition section.

DISCLOSURE OF THE INVENTION

Taking the above problems into consideration, the object of thisinvention is to provide stiffness-taper tubing and a manufacturingmethod and apparatus for such, in which the bonding strength in thetransition section between resins having different stiffness isincreased, and where the length of the transition section is shortenedin order to maintain the function of the tubing to meet the conditionsof use and improve operability, and furthermore where the volume ofresidual resin when switching resins is reduced as well as thedegradation of the quality of residual resin due to heating issuppressed.

In order to accomplish the aforementioned objectives, the presentinvention provides stiffness-taper tubing in which at least a firstresin and second resin, having differing stiffness, are joined such thatthe stiffness of the tubing gradually changes in the longitudinaldirection, and where simple surface contact in a transition sectionbetween the first resin and second resin is broken and a section whereboth resins are uniformly mixed is formed.

With this structure, by extruding and replacing resin while at the sametime mixing both resins when switching the two kinds of resins informing a transition section, a section where simple surface contact ina transition section between the first resin and second resin is brokenand a section where both resins are uniformly mixed is formed and thebonding strength is increased.

Simple surface contact is generally contact between flat or curvedsurfaces. Moreover, the section where both resins are uniformly mixed isnot only a state of completely uniform mixture, but includes a statewhere an identifiable interface such as an inclined surface orwedge-shaped interface is broken down to some extent and both resins arealternately scattered.

Moreover, this invention provides a method of manufacturingstiffness-taper tubing which uses an extrusion mold comprising a diehaving and extrusion hole, a die holder for holding this die, and amandrel that is mounted in this die holder and which fits inside theextrusion hole; and where the tubing is formed such that the stiffnesschanges gradually and continuously in the longitudinal direction byusing a first resin and second resin that have different stiffness, andwhere the first resin and second resin are mixed in a cylindrical spacethat is formed between the die holder and mandrel.

With this structure, both resins are mixed inside the cylindrical spacebetween the die holder and mandrel and which is in front of the die, soboth resins are sufficiently mixed inside this cylindrical space beforereaching the extrusion hole in the die, thus making it possible toincrease the bonding strength in the transition section. The cylindricalspace is the space formed between the inner surface of the hole formedin the die holder for inserting the mandrel and the outer surface of thecylindrical shaped mandrel. This cylindrical space improves the mixingaction, as well as makes it possible to reduce the joint-flow volume,thus making it possible to shorten the length of the transition section.

Furthermore, this invention provides an apparatus for manufacturingstiffness-taper tubing comprising a die having an extrusion hole, a dieholder for holding this die, and a mandrel that is mounted in this dieholder and which fits inside the extrusion hole; and where there are aplurality of resin-supply ports in the die holder from which resinshaving differing stiffness are switched and supplied to the mandrel inorder to form tubing such that the stiffness changes gradually andcontinuously in the longitudinal direction, and furthermore where theinsertion hole for the mandrel connects with the extrusion hole in thedie holder and the mandrel is mounted inside this insertion hole, andthe plurality of resin-supply ports open up to the cylindrical spacethat is formed between the inner surface of the mandrel insertion holeand the outer surface of the mandrel, at a position that is separated bya distance from the extrusion hole in the die, and a plurality of resinsflow together inside this cylindrical space.

With this structure, a location is formed in the cylindrical space formixing both resins, and in this space it is possible to obtain suitablemixing action, as well as it is possible to shorten the distance to thesupply ports for both resins, making it possible to reduce the amount ofresidual resin that exists at the time of switching, and suppress anychanges or deterioration in quality of the resin due to heating of theresidual resin.

In a preferred form, the mandrel inside the mandrel insertion hole is amultiple-thread screw, and the screw grooves are divided into aplurality of positions by forming the screw such that the threads, whichform the screw grooves, stop part way and then new threads start from anadjacent offset position.

With this structure, each thread groove of the multi-thread screw (screwwith two or more threads) is divided part way, and the resins in thegrooves are intricately mixed together to break down simple surfacecontact between both resins and to form a dispersed mixed state whichincreases the bonding strength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the stiffness-taper tubingmanufacturing apparatus of an embodiment of the present invention.

FIG. 2 is a schematic diagram of another embodiment of the invention.

FIG. 3 is a schematic diagram of yet another embodiment of theinvention.

FIG. 4 is a schematic diagram of still yet another embodiment of theinvention.

FIG. 5 is an expanded drawing of the embodiment in FIG. 4.

FIG. 6 is a cross-sectional view of section A—A in FIG. 5.

FIG. 7 is a schematic diagram of the prior two-layer extrusion-typeformation apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention are explained withreference to the drawings.

FIG. 1 is a schematic diagram explaining the stiffness-taper tubing ofan embodiment of the present invention.

The extrusion-type formation apparatus 1 of this stiffness-taper tubingmanufacturing apparatus comprises; a die 3 having an extrusion hole 2, adie holder 4 which holds this die 3, and a mandrel 5 that is mountedinside this die holder 4. The mandrel 5 is inserted into a mandrelinsertion hole 6 that is formed in the die holder 4 and held by the dieholder 4. The tip of the mandrel 5 fits inside a conical inlet 2 a ofthe die 3. A cylindrical space 7 is formed between the outer surface ofthe mandrel 5 and the inner surface of the mandrel insertion hole 6, andthe inner surface of the conical inlet 2 a on the extrusion hole 2.

A supply port for resin A 8 and a supply port for resin B 9 open up tothis cylindrical space 7. In addition, the position where these resinsupply ports 8, 9 open up to the cylindrical space 7 is theaforementioned mixing point C for the resins, and the outlet of theextrusion hole 2 of the die 3 is the discharge point D. The joint-flowvolume V between these points C, D can be made very small because thediameter of the cylindrical space 7 is small and the width of the spaceis thin. In this way, it is possible to reduce the time required forreplacement when switching resins and shorten the length of thetransition section.

When forming stiffness-taper tubing, first only resin A (the firstresin) is supplied from the resin A supply port 8, and the resin Asection is formed using only resin A. When doing this, the resin isdischarged from the extrusion hole 2 while pulling out a core member 10that is inserted in the center of the mandrel 5, and tubing with aninner diameter that corresponds to the diameter of the core member 10 isformed. Next, supplying of resin A stops, and only resin B (the secondresin) is supplied from the resin B supply port 9.

At this time, the previous joint-flow volume V, including thecylindrical space 7 in the die holder 4, is already filled with resin A.From this state, resin A is gradually replaced with resin B. As resin Bmoves into the cylindrical space 7 it replaces resin A. The volume ofthis cylindrical space is very small so, as described above, it ispossible to reduce the time required for replacement and shorten thelength of the transition section.

The transition section, where the resins A and B are mixed by way of thecylindrical space 7, is formed in this way, and after all of resin A hasbeen replaced by resin B in the cylindrical space 7, the resin B sectionis formed with only resin B. In this way, the stiffness-taper tubing isformed by extrusion.

In this cylindrical space 7, it is possible to add a means for activelymixing the resins while they flow. By doing so it is possible to form amixed section where the simple contact state between the resins isbroken down and the resins are uniformly mixed, and thus it is possibleto improve the bonding strength. This kind of mixing means is describedlater.

Moreover, in the embodiment shown in FIG. 1, the resin supply ports 8, 9are close to the supply sources of the resins so while one resin isbeing supplied, the volume of the other resin that remains decreases, soany possibility of changes in quality or deterioration due to heating ofthe residual resin decreases, making it possible to obtain high-qualityextrusion tubing.

The mandrel 5 is depicted in the figure as a single cylindrical memberthat is long in the axial direction, however, it is possible for the tipto be removable such that it can be replaced with a tip that fits theshape of conical inlets 2 a of various kinds of dies 3.

Also, when switching between resins A and B, it is possible to switchfrom resin A to resin B by gradually reducing the amount of resin A thatis supplied while gradually increasing the amount of resin B that issupplied in order to keep the total supplied amount of both resinsconstant.

FIG. 2 is a schematic diagram explaining another embodiment of theinvention. In this embodiment, there is a means for mixing the resinsinside the cylindrical space 7 of the embodiment shown in FIG. 1.

In this embodiment, a multiple-thread screw 11 is formed on the mandrel5 as the means for mixing the resins. Each of the supply ports 8, 9 forthe resins A, B face and open up to a different adjacent screw groove.The height of the threads gradually becomes lower as the threads advanceforward. The resins that are supplied from each of the resin supplyports 8, 9 go over the threads in the axial direction as they graduallywind forward along the respective screw grooves. By doing this both ofthe resins are actively mixed in the cylindrical space 7 between theinner surface of the mandrel insertion hole 6 and the outer surface ofthe mandrel 5 (in this embodiment the inside is a screw shape). Throughthis active mixing, any simple contact between the resins A and B isbroken down, and a section where the two resins are uniformly mixed isformed. In this way, the resins are firmly joined in the transitionsection, and the reliability of the bond is increased. The otherconstruction and effects are similar to those of the embodiment shown inFIG. 1.

FIG. 3 is a schematic diagram explaining yet another embodiment of theinvention. This embodiment shows an example of a different means formixing the resins.

In this embodiment, screws 12 a, 12 b, and 12 c are formed on themandrel 5 such that the ends of pairs of screw grooves overlap in order.The resin supply ports 8, 9 open up to the same screw groove of thefirst screw 12 a. The supplied resin spirals forward following thethreads of the first screw 12 a, then moves to the screw groove of thenext screw 12 b and moves forward, and finally moves to the screw grooveof screw 12 c and moves forward. By changing screw grooves while movingforward in a spiral motion, it is possible to improve the mixing actionof the resins when switching between resins. In this case, the height ofthe threads may gradually become lower as the threads advance forward inthe same way as in the embodiment shown in FIG. 2. The otherconstruction and effects are similar to those of the embodiment shown inFIG. 2.

In each of the embodiments described above, the mixing action can befurther improved by rotating the mandrel 5. Moreover, the number ofkinds of resins used in forming the tubing is not limited to two kinds,and it is possible to use three or more kinds of resin.

FIG. 4 is still another embodiment of the invention. This embodiment isan example of changing the screw section of the mandrel. FIG. 5 is anexpanded drawing of the embodiment and FIG. 6 is a cross-sectional viewof the section A—A in FIG. 5.

The mandrel 13 of this embodiment (only the screw section is shown) isan example of the mandrel 5 shown in FIG. 2 in which the multiple-threadscrew has been changed. Facing each starting portion of the screw groove‘a’ and the screw groove ‘b’, the supply port 8 of the first resin(resin A) and the supply port 9 of the second resin (resin B) open upfrom the die holder 4 (see FIG. 2), respectively. The screw groove ‘a’is divided into two by a thread ‘t5’ at a point of division ‘a1’. Inother words, at this point of division ‘a1’, the screw thread ‘t4’ stopspart way, and there is a new screw thread ‘t5’ that is formed adjacentto it. The screw groove ‘a’ is divided in this way.

Similarly, screw groove ‘b’ is divided into two by a screw thread ‘t6’at the point of division ‘b1’. The divided multiple-thread screw isfurther divided into two in a similar manner at points of division ‘a2’and ‘b2’. As can be seen from the figure, the screw threads, ‘t1’, ‘t3’,‘t5’, . . . , ‘t11’ that are evenly spaced from the supply port 8 in theaxial direction, are opposite from threads ‘t2’, ‘t4’, ‘t6’, . . . ,‘t12’ that are evenly spaced from the supply port 9, and are such thatthreads ‘t1’ and ‘t4’, ‘t3’ and ‘t2’, ‘t5’ and ‘t8’, ‘t7’ and ‘t6’, ‘t9’and ‘t12’ and ‘t11’ and ‘t10’ are connected. Also, screw threads (1) to(6) in cross-section A—A are connected to the threads ‘t3’, ‘t5’, ‘t7’,‘t9’, ‘t11’ and ‘t12’.

By feeding the resins through these screw grooves that have beenrepeatedly divided in this way, both resins are intricately mixed at theinterface when switching between resin A and resin B, thus breaking downthe state of surface contact and dispersing the resins such that theyare mixed uniformly or almost uniformly. The embodiment described aboveis of a double thread screw, but it is also possible to use atriple-thread or other multiple-thread screw.

INDUSTRIAL APPLICABILITY

As explained above, in this invention, the previous and later resins areadequately mixed when switching between and extruding in order thedifferent resins, so the bonding strength in the A transition section ishigh and there is no possibility of the bond coming apart, thus it ispossible to obtain highly reliable stiffness-taper tubing. In otherwords, by extruding and replacing the resin while mixing the resins inthe transition section, the resins are mixed uniformly with no inclinedsurfaces or wedge-shaped surface contact in the interface between theresins, so the bonding strength between the resins is increased.

Moreover, the volume of the mixed space after the different resins aremixed until they are discharged from the die is reduced, making itpossible to shorten the length of the transition section. Furthermore,the volume of residual resin that is waiting for the resin to beswitched is reduced, and therefore it is possible to suppress any changein quality or deterioration due to heating of the resin, making itpossible to obtain high-quality stiffness-taper tubing.

When this invention is used particularly as a medical-use catheter, thebond in the transition section between the flexible section on thedistal end, that is inserted into the body, and the stiff section at theproximal end becomes strong, so reliability of the medical equipment isincreased, and it is possible to obtain a high-quality catheter wherethe length of the transition section is long enough to maintain thecapability of being threaded through arteries while at the same is shortenough to improve operability, and where the quality of the resin in thetubing does not deteriorate.

What is claimed is:
 1. An apparatus for manufacturing stiffness-tapertubing comprising: a die having an extrusion hole, a die holder forholding said die, and a mandrel which is mounted inside said die holderand fits in said extrusion hole, and which forms stiffness-taper tubingby switching between and supplying resins having different stiffnessesover said mandrel from a plurality of resin-supply ports that are formedin said die holder such that the stiffness gradually changes in thelengthwise direction, wherein a mandrel insertion hole that connects tosaid extrusion hole is formed in said die holder and said mandrel ismounted in this mandrel insertion hole, and said plurality ofresin-supply ports open up to a cylindrical space that is formed betweenthe inner surface of said mandrel insertion hole and the outer surfaceof said mandrel at a position that is separated from the extrusion holein said die, and the plurality of resins flow together in thiscylindrical space, and wherein said mandrel in said mandrel insertionhole is formed like a screw having a thread which gradually becomeslower as the thread advances forward.
 2. The apparatus for manufacturingstiffness-taper tubing of claim 1, wherein said mandrel in said mandrelinsertion hole is a multi-thread screw that is formed such that thescrew grooves are divided up at a plurality of positions by formingthreads, that form said screw grooves, that stop part way and newthreads start at an adjacent offset position, and wherein the height ofsaid threads gradually becomes lower as the threads advance forward. 3.The apparatus for manufacturing stiffness-taper tubing of claim 1 inwhich said screw has a first thread and a second thread, and wherein anend of the first thread offsets and partially overlaps with an end ofthe second thread.